arm64/sysreg: Update system registers for SME 2 and 2.1

FEAT_SME2 and FEAT_SME2P1 introduce several new SME features which can
be enumerated via ID_AA64SMFR0_EL1 and a new register ZT0 access to
which is controlled via SMCR_ELn, add the relevant register description.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-3-f2fa0aef982f@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>